In the field of medicine, there has been an increasing need to develop implant materials for correction of biological defects. Particularly, in the field of orthopedic medicine, there has been the need to replace or correct bone, ligament and tendon defects or injuries. For example, Anterior cruciate ligament (ACL) reconstruction has become a common orthopedic procedure, with more than 200,000 ACL reconstructions being performed annually in the United States. The number of procedures involving the replacement, repair, or reconstruction of other tendons and ligaments is also increasing.
As a result, there have been development efforts relating to implants and implant materials to be used in such procedures. It is generally recognized that for implant materials to be acceptable, they must be pathogen free, and must be biologically acceptable. Some examples of synthetic implant materials include, but are not limited to, metals and polymeric substances. Some examples of non-synthetic implant materials include, but are not limited to, bone and soft tissues such as tendons and ligaments. Non-synthetic materials can be obtained from autogenic sources, allogenic sources, and xenogenic sources. The use of autograft, allograft, and xenograft bone in implants is generally desirable because these implant materials may be remodeled over time such that autogenous bone replaces the implant materials.
One way that the goal of having the bone components of an implant be remodeled over time can be achieved is by utilizing autograft bone, which is taken from a healthy harvest site within the patient and then implanted into a diseased or injured site within the same patient. However, use of autograft materials is attended by the significant disadvantage that a second site of morbidity must be created to harvest autograft for implantation into the diseased or injured site. Patients often complain about the pain and resultant effects at the harvest site. Additionally, the use of autograft materials increases procedure time and operation costs, as well as increasing the physician risk due to the handcrafting and judgment oriented aspects involved in harvesting and shaping an implant in the operating room.
In view of the disadvantages associated with the use of autograft implant materials, allograft and xenograft implant materials have been given increasing attention in recent years. Allograft materials are materials that are transplanted from genetically nonidentical individuals of the same species. For example, human allograft materials are generally recovered from cadavers and are then treated to remove pathogens prior to being implanted into live patients. Human allograft materials have the disadvantage of being frequently low in availability and high in cost of recovery, treatment and preparation for implantation. Certain highly desirable tissue types such as tendon allografts in general and bone-tendon or bone-tendon-bone grafts in particular face long standing and significant supply shortages. Demand for such tissues is difficult to measure definitively, but is believed to be at least about two to three times historically available levels of supply. Xenograft implant materials are materials that are transplanted from an animal of one species to an animal of another species. For example, bovine bone and porcine bone are two types of preferred xenograft materials for use in human patients. Such xenograft materials are readily available, but the actual use of such materials is significantly constrained due to immunological, regulatory, and disease transmission considerations and restrictions. Further, due to differences in size, structure and anatomy between species, it is sometimes difficult to locate a properly suited xenograft bone-tendon-bone implant.
In view of the foregoing considerations, it remains the case that there has been a long felt need for increased supplies of biologically acceptable implant materials to replace or correct bone, ligament and tendon defects or injuries. The present technology provides a significant advance in the art, and largely meets this need, by providing materials and methods for production of various bone-soft tissue implants from component parts to produce assembled implants.
Orthopedic medicine is increasingly becoming aware of the vast potential and advantages of using bone-tendon-bone grafts to repair common joint injuries, such as Anterior Cruciate Ligament (ACL) or Posterior Cruciate Ligament (PCL) tears. One technique that is currently used for repairing these types of injuries involves surgically reconnecting the torn portions of a damaged ligament. However, this technique is often not possible, especially when the damage to the ligament is extensive. To address situations where the damage to the joint ligaments is severe, another technique commonly performed involves redirecting other tendons within the patient's own leg to provide increased support to a damaged knee. One shortcoming of such procedures involving reconnection or redirection of tendons is that the repaired joint tends to lack flexibility and stability.
The recent utilization of bone-tendon-bone grafts has dramatically improved the results of joint repair in cases of severe trauma. Even in cases of extensive damage to the joint ligaments, orthopedic surgeons have been able to achieve up to 100 percent range of motion and stability using donor bone-tendon-bone grafts. The term bone-tendon-bone graft, sometimes also referred to as a BTB, is used for historical reasons. By definition a “tendon” is a collagenous cord that attaches muscle to its point of origin, typically to bone, and a “ligament” is a band of collagenous tissue that interconnects bone or supports viscera. Thus, it would appear that a BTB would more properly be called a bone-ligament-bone graft or implant. However, many BTBs employ a tendon, which is larger and generally more plentiful in a body. One such example is a bone-patellar tendon-bone graft, also called a BPTB, which utilizes the patellar tendon Additionally, an implant using metal, polymeric, other synthetic, or artificial bone material at either end, instead of bone, may still be referred to as being a BTB or bone-tendon-bone graft in some cases. The name bone-soft tissue graft thus more accurately encompasses the subject matter meant when the term bon-tendon-bone graft is used. Because the name BTB became adopted by the art, it is used herein to encompass all of the bone-soft tissue-bone and bone-soft tissue grafts described herein.
Despite the realized advantages associated with bone-tendon-bone grafts, there have been some difficulties encountered with utilizing currently available bone-tendon-bone grafts.
For example, U.S. Pat. No. 5,370,662 (“the '662 patent”), entitled “Suture Anchor Assembly,” which issued to Stone on Dec. 6, 1994, discloses the use of a screw made from titanium, stainless steel, or some other durable, non-degradable, biocompatible material having an eyelet at one end for attaching a suture connected to a soft material, such as a ligament or tendon. U.S. Pat. No. 5,370,662 at col. 1, lines 8-9. One problem with such a device is that the screw, although bio-compatible, will never become assimilated into the patient's body and will not be remodeled over time. A second problem is that the tendon or ligament will never form a natural attachment to the screw.
One attempt at solving these problems was disclosed in U.S. Pat. No. 5,951,560 (“the '560 patent”), entitled “Wedge Orthopedic Screw,” which issued on Sep. 14, 1999 to Simon et al. The '560 patent discloses a wedge-shaped interference screw made from a biocompatible material for use with a ligament and with two bone blocks for performing anterior cruciate ligament (ACL) repairs. In the '560 patent, a bio-compatible, wedge-shaped interference screw, a bone block and a ligament are inserted into an osseous tunnel drilled into a bone of a patient in need of a ligament repair. The interference screw compresses the flat surface of a bone block against a ligament that is pressed into the wall of the osseous tunnel. As the interference screw advances, the force that it presses against the ligament is buttressed by the force against the opposing tunnel wall. A second interference screw compresses a second bone block against an opposing end of the ligament in a second osseous tunnel drilled in a second bone in need of ligament repair. One shortcoming of this approach is that it is difficult to pull a predetermined tension on the tendon because the tendon slips in the bone tunnel and uncontrollably alters the tension when the interference screw is being threaded in the bone tunnel. The slippery ligament is also subject to slippage when compressed between the bone block and the tunnel wall. Such slippage results in a loss of tension in the joint. In the case of an ACL repair, this loss of tension causes a wobbly knee. A second shortcoming of this method is an increase in complexity, difficulty, and time required during implantation, as the components are not pre-attached and do not have any predetermined position along the length of the tendon prior to implantation. This is undesirable in any human, and particularly in athletes.
Another approach to making a BTB is disclosed in U.S. Pat. No. 5,961,520 (“the '520 patent”), entitled “Endosteal Anchoring Device for Urging a Ligament Against a Bone,” which issued to Beck, et al. on Oct. 5, 1999. Like the '560 patent, the '520 patent utilizes an interference screw and a bone block (called an “anchor body” therein) to press the end of a ligament against the side wall of an osseous tunnel in the patient's bone. The '520 patent differs from the '560 patent in that the ligament loops around the bone block in a “U” shape. This “U” shape of the tendon captures the tendon in the first bone tunnel, but leaves two free tendon ends to be secured in the second bone tunnel. In addition in the '520 patent, the bone block, which presses the ligament against the walls of the osseous tunnel contains two grooves for “locking” (col. 7, line 2) the ligament in place, and “restricting excessive compression on the ligament” (col. 7, lines 5-9). The “locking” of the tendon against the tunnel wall still leaves the tendon free to move against the tunnel wall near the ends of the anchor body. This can lead to impaired healing and recovery due to tendon to bone contact within the tunnel and also due to micromotions of the tendon within the tunnel. Ultimately, this may lead to widening of the bone tunnels rather than their closure. Additionally, the location of the tendon in the locking grooves is a function of the anchor body design and is not a controlled design parameter. Thus, the tendon placement with respect to either the tunnel wall or the tunnel centerline cannot be matched to particular surgical needs or to surgeon preference. Further, there is an increase in complexity, difficulty, and time required during implantation, as the components are not pre-attached and do not have any predetermined position along the length of the tendon prior to implantation.
Another approach to making a BTB is disclosed in U.S. Pat. No. 6,730,124 (the “'124 patent”), entitled “Bone-Tendon-Bone Assembly With Cancellous Allograft Bone Block,” which issued on May 4, 2004 to Steiner. The '124 patent is directed toward a cancellous bone block assembly with at least one tendon replacement member being extended between two cancellous bone blocks. Each substantially cylindrically shaped cancellous bone block has a central through going bore, a flat exterior longitudinal surface and a channel longitudinally cut in the exterior of the bone block body opposite the flat longitudinal surface. The tendon replacement member is inserted through the central through going bore around the end of the block and looped back along the flat longitudinal side where it is tied to the back of the tendon loop. A channel cut in the exterior surface is adapted to receive an interference screw to keep the block anchored in a bone tunnel previously cut in the respective bone. One shortcoming of this design is the very large amount of contiguous cancellous bone required to construct the bone blocks. Cancellous bone material is costly, as well as being in high demand and short supply. The hollow cylindrical geometry of a single bone block having a diameter from 8-12 mm and a length of 25-35 mm (See '124 Patent at Col. 7, lines 8-10) requires that a very large piece of bone be drilled out and cut down to make each bone block. A second shortcoming with this approach is that the through going bore cut through the bone block to accommodate the tendon limits the wall thickness of cancellous bone. The thickness of the cancellous bone wall in the end bone block is also limited by the need for the bone block to fit into a bone tunnel with the tendon also looped next to the bone block. This presents a conflict between the need to maintain the size of the bone tunnel drilled in the patient's leg, the need to provide a large enough tendon to support the loads required for successful recovery and physical therapy, and the need to provide sufficient cancellous material for structural support and fixation. Another shortcoming of this system is the relatively low pullout strength supported by the looped and sutured configuration of the '124 patent. For example, the '124 patent recites 200 Newtons as a minimum pull out force ('124 patent at Col. 8, lines 37-38) and only two of the thirteen implants reported in the testing had a failure load greater than 400 Newtons. In contrast, an article published in 1984 by Noyes et. al., entitled “Biomechanical Analysis of Human Ligament Grafts Used In Knee-Ligament Repairs and Reconstructions,” reported that failure loads of at least 445 Newtons are required of a reconstructed ACL during completion of normal activities of daily living. The Journal of Bone and Joint Surgery, Vol. 66-A, No. 3 (March 1984), pp. 344-352. Accordingly, it is desirable to provide implants that have an average strength (pull out failure load) of at least about 445 Newtons.
Yet another approach to making a BTB is disclosed in commonly assigned U.S. Pat Appl. Pub. No. 2003/0023304 (“the '304 publication”), to Carter et al., which published on Jan. 30, 2003. The '304 publication discloses several embodiments of a BTB. In each of the various embodiments, a tendon is bound in an internal chamber created in the bone blocks. For example, in FIG. 10 a plurality of cams reverse the direction of the tendon several times and cancellous chips packed in any open space bite into the tendon to keep it from slipping. In FIG. 12, a screw compresses the tendon against the side of an internal chamber. In FIG. 14, an internal wedge that has teeth bites into a tendon and tightens the grip as the tendon is pulled. In yet another embodiment, shown in FIG. 15, one end of a tendon is doubled over and the doubled over end is held in place by a series of grooves and rings. While all of these embodiments are potentially useful, they each are challenging to manufacture and/or assemble due to their inherent complexity and reliance on small or intricate parts.
One isolated and purified BTB that is not hindered by slippage or cut fibers when subjected to high tensile pulling is disclosed in commonly assigned U.S. Pat. No. 6,497,726 (“the '726 patent”) which issued on Dec. 24, 2002 to Carter et al. The '726 patent discloses the use of natural bone-tendon attachments that are cut from allograft or xenograft sources, commonly referred to as “pre-shaped” or “natural” BTBs. Typically, the BTB is cut as a single piece from a section of the patella (bone), patellar tendon and the tibia (bone) of the donor. The availability of such implants can be limited due to the limited quantity of undamaged material sources and the age requirements that are acceptable to physicians. Generally, only 2-3 grafts can be obtained per knee of the donor, depending upon the donor's age and health. In utilizing pre-shaped (natural) BTBs, some of the physical dimensions of the graft, particularly tendon length, are determined by the anatomy of the donor. Frequently, this leads to compromises such as excessive gauge length (length between the bone blocks), which result in surgical challenges and compromised healing and recovery. For example, a natural BTB with a tendon that is too long for an ACL repair results in having a length of unsecured and wobbling tendon in the bone tunnel between the ends of the secured bone portions. The wobbling tendon hinders healing in the bone tunnel.
A recent development in making BTBs was published by Dr. Seth Gasser and Dr. Reuny Uppal in “Anterior Cruciate Reconstruction: A New Technique for Achilles Tendon Allograft Preparation,” Arthroscopy: The Journal of Arthroscopic and related Surgery, Vol. 22, No. 12 (December 2006): pp. 1365.e1-1365.e3. Drs. Gasser and Uppal disclose the formation of a bone-Achilles' tendon-bone allograft by using an Achilles' allograft, which typically includes a block of calcaneus and the attached Achilles' tendon. The bone block with the natural tendon attachment used as the femoral end of the graft construct. A 25 mm long bone plug is harvested from the calcaneus with the attached Achilles' tendon. A free (unattached to the tendon) bone plug is then harvested from the remaining calcaneal bone block that measures 9 mm in diameter and 30 mm long. Three holes are drilled into the free bone plug, and the holes are used to suture the free bone plug to one side of the tendon on the tibial end of the graft construct. The formed graft is implanted and secured with interference screws in a similar fashion to a traditional bone-patellar tendon-bone ACL reconstruction. The making of BTB implants in this manner increases time spent in the operating room per procedure, which increases procedure costs, and can result in increased surgeon risk due to the fact that the surgeon is individually handcrafting each implant.
Accordingly, there is a need in the art for implants that provide a bone-tendon-bone graft that is consistently constructed to precise dimensions and is adapted for robust fixation, while allowing adherence to preferred surgical techniques. There is a further need for implants that promote reduced operating room times and reduce opportunities for error during surgery.